Boss forming process



April 17, 1945. Y 2,373,901 BOSS FORMING PROCESS Filed Nov. '9, 1940 lNVENTOk Y Wanda- 1/4254, /aw 'y.

ATTORNEYJ.

I Patented Apr. 17 1945 2,373,901 I Boss FORMING PROCESS Thomas William Lowery, Detroit, Mich., assignor to Chrysler Corporation, Highland Park, Mich., a corporation of Delaware Application November 9, 1940, Serial No. 365,134

4 Claims.

It has heretofore been the practiceto punch an aperture in a piece of plate or sheet metal before drawing the metal around the aperture thus formed into a cylindrical boss or short hollow tube of diverse cross section. The depth of draw has been limited by the occurrence of checks and cracks extending from edge portions of the metal severed during the punching operation and even in the production of shallow drawn bosses, such checking, splitting or cracking at this location has necessitated removal of considerable metal in order to trim the free end of the boss for commercial requirements.

One of the main objects of the invention is to so form, the aperture in sheet or plate metal preparatory to the boss drawing operation as to guard against the occurrence of checks and cracks at the cut edges of the metal during the boss drawing operation.

Another object of the invention isthe provision of an improved boss forming process of this kind by which a boss can be drawngto considerably greater lengths without the occurrence of checks and cracks .at the free extremity of the boss.

Another object. of the invention is the provision of an improved aperture forming step in a process of this kind which does not weakenor otherwise stress or distort the metal surrounding the aperture from which the free end part of a drawn boss is formed.

Another object of the invention is to provide for the removal of the metal surrounding a punched hole by cutting of increments of small depth therefrom in order to remove the depthwise punch scratched and strained metal without producing similar or other objectionable metal around the finalaperture and in the portion of the stock to be drawn. 1

An additional object of the invention is the pr vision of an aperture forming step in a hollow drawn boss forming process which leaves only insignificantly 'deep tool marks which do not extend depthwise, of the edge of the aperture but extend completely or partly circumferentially around the latter.

Illustrative embodiments of the invention are shown in the accompanying drawihg,.in which:

Fig. 1 is a side 'elevational view of an aperture forming tool showing the first step of the improved hollow boss forming process.

Fig. 2 is a view similar to Fig. 1 but showing the second step of the process.

. in the plate.

Fig. 3 is a fragmentary sectional view illustrating another step of the improved process by which a hollow boss is drawn from a blank apertured as shown in Figs. 1 and 2. I

Fig. 4 is a plan view of a blank provided withya punched aperture showing diagrammatically and on an enlarged scale, the effect of the punching operation upon the metal surrounding the aperture. Fig. 5 is a plan view of a blank showing an aperture formed therein in accordance with the invention. I

Fig. 6 is a perspective view of a metal plate having an integral boss formed in accordance with the invention.

Fig. 7 is a fragmentary side elevational view partly in section, of alternative apparatus which may be used to remove the metal disturbed by an aperture punching apparatus preparatory to drawing a tubular boss.

Fig. 8 is a fragmentary side elevational view,

.partly in .section, of apparatus by which a punched aperture may be formed in an operation preceding that illustrated in Fig. 8.

In the form of the invention illustrated in Figs. 1 to 3 of the drawing, a hollow tubular boss is formed integral on a sheet or plate metal blank l0 by the following steps. The blank I0 is placed upon a supporting die ll having an aperture l2 therein of somewhat larger diameter than the diameter of an aperture which is initially punched The initial aperture is formed by a tool, generally designated by the numeral I3, having a body portion I4 and a punch member I5 provided on its leading end. The punch mem ber 15 has a. protruding pointed centering element IS. The intermediate portion of the body part of the tool 13 has spiral drill-like cutting blades ll extending laterally beyond the maximum diameter of the punch member l5. Provided on the opposite extremity of the body portion of the tool I3 is a shank I8 having flattened surfaces I!) by which the tool may be non-rotatably clamped in a chuck, press or similar device. During the initial operation the punch member l5 forms an undersized aperture inthe blank ll] of smaller diameter than the passage l2 of the die II.

The metal of the blank I'll, as illustrated in Fig.

4, surrounding the initial punched aperture is marks or scratches are frequently of only slight depth, they so weaken the metal surrounding the initial punched aperture as to cause severe cracking around the free extremity of a tubular boss drawn from the metal of the blank bordering the aperture. In the practice of the present invention, all of the metal surrounding the initial punched aperture which has been so afiected by the punching operation is removed without forming other tool marks extending depthwise of the aperture. This may be accomplished by merely drilling out the undersized aperture to the final desired diameter with a conventional metal drill. In such an operation any tool marks which remain extend circumferentially of the wall of the final aperture and do not cause cracking and checking during the boss drawing operation.

Substantially the same results may be obtained by broaching away the metal surrounding the initially punched aperture in the manner illustrated in Fig. 2. When this operation is conducted with a tool of the type shown in Figs. 1 and 2, the broaching step may follow the punching operation in rapid succession and after the punching member [5 has formed the initial aper ture, the portion of the tool having the spiral cutting blades I1 thereon may be forced through the initial aperture during the same stroke of the tool in which the latter is punched. The portion of the tool on which the spiral cutting blades are formed may have a slight taper, from a minimum diameter at the end thereof adjacent the punch member I5 to a maximum diameter adjacent the shank end of the tool. The tool l3 may be held against rotation relative to the work during this step of the operation or it may be drivingly rotated in a drill-like manner.

If desired, the initial aperture may be formed by the conventional punch and die 2| and 22 illustrated in Fig. 8 and the metal surrounding the initially punched aperture may be removed by a conventional broach 23 as illustrated in Fig. 7. The broach 23 is preferably so constructed as to cut away successively small portions of metal in order to avoid formation of depthwise extending tool marks and scratches in the wall surrounding the final aperture,

After the initial aperture has been enlarged wall 24, illustrated in Fig. 5, is substantially free from tool'marks of sufficient depth to cause checking and cracking during the boss drawing operation. When the enlargement of the initially formed aperture is made by a drill or by a broach having spiral cutting blades, as illustrated in Figs. land 2, any tool marks which remain extend circumferentially of the wall of the aperture or transversely of the depth of the latter.

When a blank pressed in this manner is subjected to a boss drawing operation such as that illustrated in Fig. 3 wherein a punch 25 presses the metal surrounding the aperture into a die 26, the extremity 27 of the resultin boss 28 does not crack or become serrated. T ular bosses of substantially greater length may be formed from sheet or plate metal blanks prepared in the foregoing manner without requiring removal of excessive amounts of metal from the free ends of the bosses.

Although but several specific embodiments of the invention are herein shown and described, it will be understood that various changes in the size, shape and arrangement of parts may be made without departing from the spirit of the inventlon'.

I claim:

1. The process of forming a tubular boss on a fiat portion of a sheet or plate metal blank which comprises forming an aperture in said flat portion having a bounding wall of undisturbed metal substantially free from depthwise extending shear lines and scratches by initially forming by a punch an undersized hole in said blank and subsequently enlarging said hole by cutting away successive portions of the metal surrounding the undersized hole along shear lines extending transversely of the thickness of said blank with spiral cutting elements provided on the lateral sides of said punch during continuation of the punching stroke thereof, and drawing the metal surrounding the resulting enlarged aperture to the form of a tubular boss.

2. The process of forming a tubular boss on a flat portion of a sheet or late metal blank which comprises forming an aperture in said flat portion having a bounding Wall of undisturbed metal substantially free from depthwise extending shear lines and scratches by initially forming by a punch an undersized hole in said blank and subsequently enlarging said hole by cutting away successive portions of the metal surrounding the undersized hole along shear lines extending transversely of the thickness of said blank with spiral cutting elements provided on the lateral sides of said punch by rotating the latter as a drill, and drawing the metal surrounding the resulting enlarged aperture to the form of a tubular boss.

3. The process of forming a tubular boss on a sheet metal blank which comprises the steps of punching an undersized aperture in said blank preparatory to drawing the'metal surrounding it to the form of a tubular boss and so as to admit access by a cutting tool to the metal which in the finished product comprises the free extremity of said boss, enlarging said aperture and simultaneously removing from the metal of the wall portion thereof punch formed scores and tool marks by progressively shearing from successive portions of the entire extent of said wall small increments of the metal thereof, and drawing the metal surrounding the resulting enlarged aperture in the direction of the axis of the latter to the form of a tubular boss.

4. The process of forming a tubular boss on a sheet metal blank which comprises the steps of punching an undersized aperture in said blank preparatory to drawing the metal surrounding it to the form of a tubular .boss and so as to admit access by a cutting tool to the metal which in the finished product comprises the free e-xtremity of said boss, enlarging said aperture and simultaneously removing from the metal of the wall portion thereof punch formed scores and tool marks by progressively shearing from successive portions of the entire extent of said wall small increments of the metal thereof along shear lines extending transversely of the thickness of said blank, and drawing the metal surrounding the resulting enlarged aperture in the direction of the axis of the latter to the form of a tubular boss.

THOMAS WILLIAM LOWERY. 

